TypedArray subclass pages say contents are initialized to 0

[rhashimoto]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array

What specific section or headline is this issue about?

main heading

What information was incorrect, unhelpful, or incomplete?

For each of BigInt64Array, BigUint64Array, Float32Array, etc. (all the TypedArray subclasses), the initial description contains:

The contents are initialized to 0. [or 0n]

This initialization is only done if the TypedArray subclass is created by passing a length to the constructor. It is not done if the instance is created from an existing array or a buffer.

Try this in a console:

const b0 = new Uint8Array([42]);
const b1 = new Uint8Array(b0.buffer);
console.log(b1[0]);  // <= prints 42, *not* 0

What did you expect to see?

It should say something like:

The contents are initialized to 0 [or 0n for BigInt64Array or BigUint64Array] if constructed with only a length.

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/web/javascript/reference/global_objects/float32array
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/float32array/index.md
• Last commit: e01fd62
• Document last modified: 2023-09-07T01:45:56.000Z

[Josh-Cena]

It should say "initialized to 0 unless an existing buffer is provided".

[rhashimoto]

It should say "initialized to 0 unless an existing buffer is provided".

That isn't quite correct, either. For example:

new Uint8Array([1, 2, 3]);

Here a buffer is not provided and the array is not initialized to 0.

Changing it to "existing buffer or array" is closer but still not exactly right, e.g.:

new Uint8Array(new Set([1, 2, 3]));
new Uint8Array((function*() { yield 1; yield 2; yield 3; })());

Maybe "initialized to 0 unless an existing buffer or initialization data is provided"?

[Josh-Cena]

Yeah, you are right. "unless initialization data is explicitly provided" sounds better.